Heretofore, various improvements for diminishing noise generated during operation of chain have been made as to the plate of a silent chain for use in an engine. For example, in Japanese Patent Laid Open No. 159446/94, a protruding portion, for interference with a toothed surface of a sprocket at the time of engagement of a plate of a silent chain with the toothed surface of the sprocket, is formed on the tip end side of a flank portion of the plate.
More particularly, as shown in FIG. 4, a protruding portion D is formed on the tip end side of a flank portion F of a plate P which comes into engagement with a toothed surface T of a sprocket S. The protruding portion D interferes with the toothed surface T of the sprocket S when the plate P, which is a part of a silent chain, starts into engagement with the toothed surface T of the sprocket S. Then, the other side of the flank portion F opposite the protruding portion D comes into contact and engagement with the toothed surface T. This engagement of the other side of the flank portion F opposite the protruding portion D with the toothed surface T of the sprocket S is continued until the plate P leaves the sprocket S.
In the silent chain of the above-described construction, since the protruding portion D comes into engagement with the toothed surface T of the sprocket S at the beginning of the engagement of the plate P with the toothed surface T of the sprocket S and in advance of engagement of the flank portion F with the toothed surface T of the sprocket S, a shock of engagement is buffered. Besides, since the height of engagement changes, a chordal oscillation of the chain is prevented and hence, it is possible to diminish the resulting noise.
However, the toothed surface of a sprocket which comes into engagement with a silent chain will vary depending on whether the silent chain is assembled entirely by using plates each having the aforesaid protruding portion or whether the silent chain is assembled in such a manner that the plates each having the aforesaid protruding portion are arranged only in several specific positions each between adjacent normal plates, even if either silent chain is fabricated at the same pitch as that of a silent chain assembled using normal plates not having any such protruding portion.
Therefore, it is necessary to fabricate plural types of sprockets conforming to plural types of silent chains. For example, when sprocket teeth are formed with a hob cutter, it is required in gear cutting that the addendum modification coefficient be changed for each type of a silent chain. Thus, there arises the problem that the sprocket fabricating process and stock management become complicated.
Accordingly, it is an object of the present invention to provide a plate of a silent chain capable of reducing an engagement noise and applicable to a sprocket which is used for an ordinary type of a silent chain.